Does anyone have any ideas concerning the modification of cheap (brownie-type) box cameras, particularly the lense quality, and perhaps the shutter speeds?
Has anyone built their own improved version?
I've seen things more or less like this, but they usually weren't modified from a cardboard Ansco Shur-Shot or Kodak Brownie 620 -- there have been many "box" cameras built specifically to use a particular lens with less effort than folding a bellows and building a field camera. Often they're just one box telescoped into another, with some kind of light trap where the two pieces slide; lens hard mounted in the front box, and a spring back off an old dead press camera or similar at the back.
One of the issues with modifying a box camera is that the lens is quite often buried fairly deep inside the "box" that forms the camera's body. In a Shur-Shot Jr. (of which I have one and have shot it recently), the lens (a reverse meniscus, convex toward the film) is about 1/4 of the box length back from the front plate, mounted on the back side of the (wood!) board that forms the main rigid core of the box. To replace it with, say, a 105 mm triplet in shutter, you'd have to remove the original lens entirely, bore out the hole in the central board, mount the shutter with lens into the front plate (and make provision for focusing, if it isn't already a front-cell focus type) -- and set the infinity correctly.
And the main thing you'd gain, in this case, is more versatility in exposure. That single element reverse meniscus was used in simple cameras for almost a century
because it worked. Kodak sold them (in the Brownie Hawkeye and probably other models) at least into the 1960s. A pair of such lenses, concave toward each other, properly spaced and with the aperture and shutter halfway between, could do even better at a faster aperture (I have a Speedex Jr. with that kind of lens -- fixed focus, one shutter speed plus B, choice of two aperture stops; you can count bricks in a wall from a block away or further in the images). A hundred and forty years ago, that was called a Rapid Rectilinear -- but in the 1950s, Ansco sold it as a folding box camera.